Epitaxial lateral overgrowth of (1122) semipolar GaN on (1100) m-plane sapphire by metalorganic chemical vapor deposition

The authors report the growth of semipolar (1122) GaN films on nominally on-axis (1010) m-plane sapphire substrates using metal organic chemical vapor deposition. High-resolution x-ray diffraction (XRD) results indicate a preferred (1122) GaN orientation. Moreover, epitaxial lateral overgrowth (ELO) of GaN was carried out on the (1122) oriented GaN templates. When the ELO stripes were aligned along [1120]_sapphire, the Ga-polar wings were inclined by 32° with respect to the substrate plane with smooth extended nonpolar a-plane GaN surfaces and polar c-plane GaN growth fronts. When compared with the template, the on-axis and off-axis XRD rocking curves indicated significant improvement in the crystalline quality by ELO for this mask orientation (on-axis 1700 arc sec for the template, 380 arc sec for the ELO sample, when rocked toward the GaN m axis), as verified by transmission electron microscopy (TEM). For growth mask stripes aligned along [0001]_sapphire with GaN m-plane as growth fronts, the surface was composed of two {1011} planes making a 26° angle with the substrate plane. For this mask orientation XRD and TEM showed no improvement in the crystalline quality by ELO when compared to the non-ELO template.